The most important feature of a microphone is a function to amplify a sound and a function to measure directionality of the sound.
Since there have been many researches into the function to amplify the sound from the past, there is no big problem. However, as for the function to measure the directionality of the sound, in the related art, two independent microphones without the function to measure the directionality of the sound are spaced apart from each other at a predetermined distance to measure the directionality of the sound by measuring a difference of sound pressure and a phase difference of sound waves according to a direction of the sound wave. In this case, when the distance between two microphones is very short, signals of the two microphones are very similar to each other, and as a result, it is almost impossible to find the directionality of the sound.
In particular, since a low-frequency sound has a long wavelength, it is further difficult to distinguish phases of the sound waves. For this reason, miniaturization of the microphone having the function of the directionality has a limit.